Decide to stop explosive device (9)
I believe the answer is:
determine
'decide' is the definition.
('determine' can be a synonym of 'decide')
'stop explosive device' is the wordplay.
'stop' becomes 'deter' (I've seen this before).
'explosive device' becomes 'mine' (mine is a kind of explosive device).
'deter'+'mine'='DETERMINE'
'to' acts as a link.
(Other definitions for determine that I've seen before include "Establish" , "Dictate" , "Choose" , "I'm entered, so find our precisely" , "Learn" .)